Highly Luminescent Metal Clusters Confined in Zeolites

The synthesis of functional metal clusters has attracted the attention of scientists from diverse fields over the past decades, due to promising optical properties associated with such structures, particularly their luminescence properties. However, the synthesis of sub-nanometer metal clusters consisting of few atoms is not straightforward due to the tendency of the clusters to aggregate, and thus rapidly losing their peculiar optical features. One strategy to achieve the stabilization of luminescent metal clusters is the use of zeolite frameworks that possess the appropriate molecular-sized pores and cages to confine metal clusters. Their cation-exchange capacities facilitate the uptake of metal ions, and after an activation procedure (heat treatment, photoactivation, X-ray irradiation), the formation of highly luminescent metal clusters is promoted, whose size and optical properties are controlled by the confinement environment. In this chapter, an up-to-date overview of synthesis strategies to stabilize luminescent metal clusters (particularly silver clusters) will be given, emphasizing the use of zeolites as confinement scaffolds. Moreover, several characterization strategies utilized in the study of silver clusters confined in zeolites will be discussed, focusing on the challenging nature of this task and the need for combinatorial approaches. Finally, emerging applications of luminescent silver-zeolite systems will be discussed.